(80-60)x+[(6900-60x)÷40]×10≥6900×0.320x+(6900÷40-60x÷40)×10≥207020x+(345/2-3/2x)×10≥207020x+345/2×10-3/2x×10≥207020x+1725-15x≥20705x+1725≥20705x≥2070-17255x≥345x≥345÷5x≥69
